Final answer:
Mary's earnings increase by $1.50 each day. By Thursday, this results in an additional $4.50 over Monday's earnings. Therefore, Mary will earn $26.10 on Thursday.
Step-by-step explanation:
Mary works as an English tutor and her earnings increase by a certain amount each day. On Monday, she earned $21.60. According to the information given, her daily earnings increase by $1.50 each day. Since Thursday is three days after Monday, we will calculate her earnings for Thursday step by step.
First, calculate the total increase over three days: $1.50 increase/day × 3 days = $4.50.
Then, add the total increase to Mary's earnings on Monday: $21.60 Monday earnings + $4.50 increase = $26.10.
Therefore, Mary will earn $26.10 on Thursday.